According to these guys :
Start DVDA. File menu/new. Choose single movie.
look for your video file, and open it.
Let's call it Zachs video
Now you have your vide file in your DVDA project.
Select your video (on the left side click on zachs video).
Then on the right side under media properties look for "end action", select it by clicking, then under it set command to "link", then "destination" to zachs video.
Ready to go, prepare this DVD and it must loop zachs video forever :)))